In U.S. Pat. No. 5,205,995, there is described the metathesis of by-product sodium sesquisulfate from a chlorine dioxide generation process to recover acid values therefrom while not significantly increasing the evaporative load on the chlorine dioxide generator when the recovered acid values are recycled to the chlorine dioxide generator.
One of the agents described as being employed in the process is water but, in order to minimize water usage and consequent evaporative load on the generator, it is necessary to employ, as seen in FIG. 3 of that patent, two filters, a mixing tank and recycle of part of the resulting acidic solution to the first filter.